#include<iostream>
#include"Sales_item.h"
int main()
{
	Sales_item item1, item2;
	std::cin >> item1 >> item2;
	//首先检查item1和item2是否表示相同的书
	if (item1.isbn() == item2.isbn())
	{
		std::cout << item1 + item2 << std::endl;
		return 0;                                                  //表示成功
	}
	else
	{
		std::cerr << "Data must refer to same ISBN" << std::endl;  //表示失败
		return -1;
	}
}
